Lasers whose wavelength of emitted radiation is tunable within a certain range are utilized in various semiconductor laser applications such as, for example, in optical communications technology for heterodyne reception or wavelength multiplex. The aim is to realize the tunability not via slow thermal effects, but with fast electro-optical effects. One method of wavelength tuning is to shift the refractive index in a part of the light-conducting semiconductor material resulting from charge carriers.
Presently, electrically tunable lasers exist in configurations wherein opto-electron active stripe-shaped semiconductor regions are arranged in succession in the direction of the guided light. At least one region is fashioned as a semiconductor laser. The refractive index in at least one additional region is modified, for example, by injecting charge carriers into the light-guiding strips, thus producing a change in the emitted wavelength. Instead of being arranged in succession, the laser and tuning region can also be arranged on top of one another. No arrangement is known wherein this principle of a laser zone and a tuning zone arranged on top of one another is used in a laser structure having a ridge waveguide.
European reference EP No. 0 173 269 A2 discloses a semiconductor laser structure wherein an active region is present in a longitudinal arrangement between a first control region and a second control region each of which is provided with electrodes for control. The tuning of this semiconductor occurs by a continuous variation of the current intensities supplied to these tuning electrodes.
An article by N. K. Dutta et al, "Continuously Tunable Distributed Feedback Laser Diode", Appl. Phys. Lett. 47, 981-983, 1985, discloses a tunable semiconductor laser wherein a substrate of InP acts as a thermoelectric element whose components are formed by upper and lower contacts on the substrate. A temperature difference between these two components can be produced by the Peltier effect when a current is applied to both of these contacts. The functioning of the tuning in this structure is thus composed of a combination of resistance heating and Peltier cooling.
European reference EP No. 0 297 654 A1 discloses a semiconductor laser whose layer structure allows the injection of high-energy electrons into the active layer. A shorter wavelength of light emitted by this laser is thus achieved.
European reference EP No. 0 296 066 A2 discloses a semiconductor laser that has a MQW-layer arranged transversely relative to the actual active layer. During operation of the laser, a blocking voltage with which the electrical field in this MQW-layer is controlled is applied to one MQW-layer via a separate contact and the wavelength can be varied in this fashion.